Child custody

My SO has a kid with his ex wife a daughter. When they got a divorce she told the judge she just wanted the full custody and that the state can decide on everything else. So their visitations is based on what the state granted. Well since he’s suppose to have her 4 weeks out of the summer that’s the legal right for him she hasn’t followed thru and told us we can have her a week before school starts for that week. Today when we are suppose to get her she said she had some even going on and won’t be able to come with us. We live 4 hrs away and she won’t drive half way or anything and we have to go all the way to get her and bring her back. What can we do?